1. Field of the Invention
The present invention generally relates to image processing methods, image processing apparatuses and storage media, and more particularly to an image processing method and an image processing apparatus which expand image compressed codes, and to a computer-readable storage medium which stores a computer program for causing a computer to expand image compressed codes.
2. Description of the Related Art
Due to progresses made in image input techniques and image output techniques, demands for high-definition images have increased considerably in recent years. For example, in the case of digital cameras that are used as image input apparatuses, there are high-performance digital cameras even in the popular price range, because the cost of high-performance charge coupled devices (CCDs) having over 3,000,000 pixels has decreased. CCDs having over 5,000,000 pixels will probably be realized in the near future. It is anticipated that such a trend, that is, the tendency of the number of pixels of the CCDs to increase, will continue.
On the other hand, there are demands to realize the high-definition and the low cost also in the field of hard copy apparatuses and soft copy apparatuses. The hard copy apparatuses include image output apparatuses such as laser printers, ink-jet printers, thermal printers and the like. The soft copy apparatuses include flat-panel display apparatuses such as cathode ray tubes (CRTs), liquid crystal displays (LCDs), plasma display panels (PDPs) and the like.
Processing of high-definition images has become popular due to the development of such high-performance and low-cost image input apparatuses and image output apparatuses, and it is expected that the demand for high-definition images will further increase in the future. Actually, the development of network-related technologies including personal computers and the Internet is in effect accelerating such trends. Recently, mobile (or portable) equipments such as portable telephone sets and portable personal computers have become particularly popular, and high-definition images are frequently transmitted from and received at various locations using a communication means.
As a result, it is expected that the demands to improve image compression and expansion techniques will increase further so as to facilitate processing of the high-definition images.
As one image compression technique that satisfies such demands, a technique called JPEG2000, has been proposed and is being standardized. The JPEG2000 enables restoration of high-quality images even at a high compression ratio. The JPEG2000 divides the image into rectangular regions called tiles, and carries out the compression and expansion process in units of tiles, so that the processes may be carried out using a relatively small memory capacity. In other words, the compression and expansion process can be carried out independently in units of tiles.
One frame of the JPEG2000 image may be displayed consecutively at a predetermined frame rate, so as to display a dynamic image. The frame rate refers to a number of frames that is reproduced per unit time. An international standard called Motion JPEG2000 has been proposed which displays the dynamic image by successively displaying the JPEG2000 images.
However, the JPEG2000 and the Motion JPEG2000 are not yet complete, and various problems have yet to be solved before actually reducing such standards into practice.
For example, when irreversibly compressing a master image data by the JPEG2000 or the Motion JPEG2000 and distributing the compressed image data, a receiving end, which receives the compressed image data, is unable to know a relative picture quality of an image that is obtained by expanding the compressed image data with respect to the master image.
If picture quality information were distributed in addition to the compressed image data, it would be possible to know the relative picture quality of the expanded image with respect to the master image. However, it would be necessary in this case to set a new transmission and reception protocol to enable the exchange of the picture quality information between the distributing source and the receiving end (distributing destination), and there is a problem in that the protocol will become complex.
Furthermore, if a relative picture quality difference of the expanded image with respect to the master image is small, there was a problem in that it is difficult to subjectively see the picture quality difference.